SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

[Rule 13d-101]

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO § 240.13d-1(a)

AND AMENDMENTS THERETO FILED PURSUANT TO § 240.13d-2(a)

(Amendment No. 12)*

Clearwire Corporation

(Name of Issuer)

Class A Common Stock

(Title of Class of Securities)

18538Q105

(CUSIP Number)

David K. Schumacher

General Counsel

Crest Financial Limited

JP Morgan Chase Tower

600 Travis, Suite 6800

Houston, TX 77002

Tel: (713) 222 6900

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

Copies to:

Stephen M. Gill

Kai Haakon E. Liekefett

Vinson & Elkins LLP

First City Tower

1001 Fannin Street, Suite 2500

Houston, TX 77002

Tel: (713) 758 2222

May 10, 2013

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (the “Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

(Continued on following pages)

This Amendment No. 12 (this “Amendment”) amends and supplements the Statement on Schedule 13D (the “Schedule 13D”) of Crest Financial Limited (“CFL”), Crest Investment Company (“CIC”), the Jamal and Rania Daniel Revocable Trust (the “Jamal and Rania Daniel Trust”), Mr. Jamal Daniel, Mrs. Rania Daniel, DTN LNG, LLC (“DTN LNG”), DTN Investments, LLC (“DTN Investments”), the Daria Daniel 2003 Trust (the “Daria Daniel Trust”), the Thalia Daniel 2003 Trust (the “Thalia Daniel Trust”), the Naia Daniel 2003 Trust (the “Naia Daniel Trust”), Mr. John M. Howland, Mr. Eric E. Stoerr, the Halim Daniel 2012 Trust (the “Halim Daniel Trust”), Mr. Michael Wheaton, solely in his capacity as trustee of the Halim Daniel Trust, Mr. Halim Daniel, Uniteg Holding SA (“Uniteg”) and Crest Switzerland, LLC (“Crest Switzerland” and, together with CFL, CIC, the Jamal and Rania Daniel Trust, Mr. Jamal Daniel, Mrs. Daniel, DTN LNG, DTN Investments, the Daria Daniel Trust, the Thalia Daniel Trust, the Naia Daniel Trust, Mr. Howland, Mr. Stoerr, the Halim Daniel Trust, Mr. Wheaton, solely in his capacity as trustee of the Halim Daniel Trust, Mr. Halim Daniel, Uniteg and Crest Switzerland, the “Reporting Persons”) that was filed in respect of Clearwire Corporation (the “Issuer”) on June 1, 2012 and amended by Amendment No. 1 filed on November 7, 2012 (“Amendment No. 1”), Amendment No. 2 filed on December 18, 2012 (“Amendment No. 2”), Amendment No. 3 filed on March 13, 2013 (“Amendment No. 3”), Amendment No. 4 filed on March 20, 2013 (“Amendment No. 4”), Amendment No. 5 filed on April 4, 2013 (“Amendment No. 5”), Amendment No. 6 filed on April 9, 2013 (“Amendment No. 6”), Amendment No. 7 filed on April 11, 2013 (“Amendment No. 7”), Amendment No. 8 filed on April 23, 2013 (“Amendment No. 8”), Amendment No. 9 (“Amendment No. 9”) filed on April 25, 2013, Amendment No. 10 filed on May 7, 2013 (“Amendment No. 10”) and Amendment No. 11 filed on May 9, 2013 (“Amendment No. 11”).

Item 4 of the Schedule 13D is hereby amended and supplemented by adding the following paragraphs after the first paragraph thereof:

On May 10, 2013, CFL told its brokerage firms to take all necessary steps to perfect its rights under Section 262 of the Delaware General Corporation Law to seek appraisal for the common stock of the Issuer that it beneficially owns and issued a press release relating thereto (the “Press Release”), a copy of which is attached hereto as Exhibit 2 and is incorporated herein by reference.

Item 6 of the Schedule 13D is hereby amended and restated in its entirety as follows:

Other than Asset Purchase Agreement as described in Item 3 hereof (which has been fully performed by the parties thereto in 2004), the Joint Filing Agreement attached hereto as Exhibit 1, the Press Release attached hereto as Exhibit 2, the Presentation to Stockholders attached to Amendment No. 11 as Exhibit 2, the Press Release attached to Amendment No. 11 as Exhibit 3, the Press Release attached to Amendment No. 10 as Exhibit 2, the Letter to Stockholders attached to Amendment No. 10 as Exhibit 3, the Power of Attorney for the Daria Daniel Trust attached to Amendment No. 10 as Exhibit 4, the Power of Attorney for the Thalia Daniel Trust attached to Amendment No. 10 as Exhibit 5, the Power of Attorney for the Naia Daniel Trust attached to Amendment No. 10 as Exhibit 6, the Power of Attorney for John M. Howland attached to Amendment No. 10 as Exhibit 7, the Press Release attached to Amendment No. 9 as Exhibit 2, the Power of Attorney for the Jamal and Rania Daniel Trust attached to Amendment No. 9 as Exhibit 3, the Power of Attorney for Jamal Daniel attached to Amendment No. 9 as Exhibit 4, the Power of Attorney for Rania Daniel attached to Amendment No. 9 as Exhibit 5, the Power of Attorney for Eric E. Stoerr attached to Amendment No. 9 as Exhibit 6, the Power of Attorney for the Halim Daniel Trust attached to Amendment No. 9 as Exhibit 7, the Power of Attorney for Halim Daniel attached to Amendment No. 9 as Exhibit 8, the Power of Attorney for Michael Wheaton attached to Amendment No. 9 as Exhibit 9, the Power of Attorney for Uniteg attached to Amendment No. 9 as Exhibit 10, the Board Letter attached to Amendment No. 8 as Exhibit 2, the April 23 Press Release attached to Amendment No. 8 as Exhibit 3, the April 22 Press Release attached to Amendment No. 8 as Exhibit 4, the FCC Letter attached to Amendment No. 8 as Exhibit 5, the Press Release attached to Amendment No. 7 as Exhibit 2, the Press Release attached to Amendment No. 6 as Exhibit 2, the FCC Letter attached to Amendment No. 6 as Exhibit 3, the Letter to the Board attached to Amendment No. 5 as Exhibit 2, the April 3 Press Release attached to Amendment No. 5 as Exhibit 3, the Demand Letter attached to Amendment No. 4 as Exhibit 2, the March 20 Press Release attached to Amendment No. 4 as Exhibit 3, the March 12 Press Release attached to Amendment No. 3 as Exhibit 2, the FCC Letter attached to Amendment No. 3 as Exhibit 3, the Press Release attached to Amendment No. 2 as Exhibit 2, the Stockholder Letter attached to Amendment No. 1 as Exhibit 2 and the Press Release attached to Amendment No. 1 as Exhibit 3, neither the Reporting Persons nor, to the best of the Reporting Persons’ knowledge, any person named on Schedule A hereto, has any contracts, arrangements, understandings or relationships (legal or otherwise) among the persons named in Item 2 and between such persons and any person with respect to any securities of the Issuer, including but not limited to, transfer or voting of any of the securities, finder’s fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies.

The following documents are filed as exhibits:

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: May 13, 2013

EXHIBIT INDEX

Exhibit 1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the Class A Common Stock of Clearwire Corporation and further agree that this Joint Filing Agreement be included as an Exhibit to such joint filings. In evidence thereof, the undersigned, being duly authorized, have executed this Joint Filing Agreement this 13^th day of May, 2013.

Exhibit 2

FOR IMMEDIATE RELEASE:

CONTACT: Jeffrey Birnbaum, (202) 661-6367, JBirnbaum@BGRPR.com

Crest Financial Takes First Step to Perfect Appraisal Rights of Clearwire Shares

Glass, Lewis Agrees with Crest to Reject Sprint-Clearwire Merger

Crest Recommends That All Holders Vote “AGAINST” Merger Proposal

HOUSTON, May 10, 2013—Crest Financial Limited, the largest of the independent, minority stockholders of Clearwire Corporation (NASDAQ: CLWR), has told its brokerage firms to take all necessary steps to perfect Crest’s rights under Section 262 of the Delaware General Corporation Law to seek appraisal for the common stock of Clearwire Corporation that it beneficially owns.

The Delaware law permits Clearwire shareholders electing to exercise their appraisal rights to ask the Delaware Court of Chancery to determine the fair value of their Clearwire common stock if the Sprint-Clearwire merger is consummated and certain other conditions are satisfied. The law states that a Clearwire stockholder that votes FOR the Sprint-Clearwire merger cannot elect to exercise its appraisal rights.

David Schumacher, general counsel of Crest, said: “Crest will vote AGAINST the proposed Sprint-Clearwire merger. We are taking this action today to preserve our rights to an appraisal by the Delaware court. The law prevents Clearwire stockholders that vote FOR the merger from seeking fair value for their shares through an appraisal action. Therefore, those Clearwire shareholders that vote FOR the merger will not be able to participate in, or benefit from, a recovery in any appraisal action. We are optimistic that the court will decide that the fair value of Clearwire’s common stock is significantly higher than the $2.97-a-share that Sprint is offering for it.”

Crest has long argued that the price Sprint Nextel Corporation is offering to pay Clearwire stockholders for their shares is highly inadequate, that the merger was structured in a way that unfairly disadvantages minority stockholders and that Clearwire would be better off if it remained a stand-alone company.

Crest also commended Glass, Lewis & Co., a leading proxy advisory firm, for its recommendation urging that Clearwire stockholders vote against the proposed merger with Sprint. Crest said is strongly disagreed with the view of ISS that the Sprint-Clearwire merger should succeed.

Schumacher said: “Crest Financial strongly disagrees with the recommendation of ISS. As we have said and, we believe, demonstrated, Clearwire would be far stronger and would provide more value for its shareholders if were to remain a stand-alone company. We believe that Clearwire’s board and management have agreed to sell Clearwire at a price that significantly undervalues Clearwire’s spectrum assets and they have not acted in the best interests of Clearwire’s stockholders other than Sprint.

“In sharp contrast, Glass, Lewis & Co., an important proxy advisory firm, agrees with Crest that Sprint’s offer is not the best possible alternative available to Clearwire and its shareholders, that Sprint’s offer undervalues Clearwire and that stockholders of Clearwire should reject the Sprint merger offer. We are particularly baffled by ISS’s analysis regarding the actions of the Clearwire board in seeking alternatives when Charlie Ergen of DISH Network, who provided Clearwire with a possible alternative to the Sprint transaction, yesterday characterized DISH’s dealings with the Clearwire board as a game of ‘Whac-a-Mole,’ in which ‘every time we answered a question, something else popped up.’”

Masayoshi Son, Chief Executive of SoftBank, has made a number of public statements recently regarding the SoftBank-Sprint merger and the Sprint-Clearwire merger. It was reported in a Dow Jones Newswire story that Son would not expect Sprint to allow Clearwire’s board to consider bankruptcy and that Sprint would continue to finance Clearwire after a negative vote. Following this report, Crest’s Schumacher said: “Crest firmly believes that the Clearwire board must act in the best interests of all Clearwire shareholders. We believe that Son’s statements demonstrate that, if the Clearwire shareholders reject the Sprint-Softbank merger, SoftBank and Sprint intend to use Sprint’s position as Clearwire’s majority shareholder to make decisions regarding the future of Clearwire that are in the best interests of only Sprint and SoftBank and not in the best interests of all Clearwire shareholders. If Clearwire’s shareholders reject the Sprint-Clearwire merger as we expect, Crest will aggressively protect its rights as a minority shareholder in Clearwire.”

Schumacher concluded: “Crest will continue to aggressively wage its proxy fight against the Sprint-Clearwire merger. We are extremely pleased with the number of holders who have reached out to us in support of our efforts. Over the next week, Crest looks forward to speaking to all holders to urge them to use the GOLD proxy card and vote “AGAINST” the Sprint-Clearwire merger.”

D.F. King & Co, Inc. has been retained by Crest to assist it in the solicitation of proxies in opposition to the merger. If stockholder have any questions or need assistance in voting the GOLD proxy card, please call D.F. King & Co. at (800) 949-2583. The proxy statement can be found at http://www.dfking.com/clwr.

About Crest Financial Limited

Crest Financial Limited (“Crest”) is a limited partnership under the laws of the State of Texas. Its principal business is investing in securities.

Important Legal Information

In connection with the proposed merger of Clearwire with Sprint Nextel Corporation (the “Proposed Sprint Merger”), Crest and other persons (the “Participants”) have filed a definitive proxy statement with the U.S. Securities and Exchange Commission (“SEC”). The definitive proxy statement will be mailed to the stockholders of Clearwire on or about May 6, 2013. SECURITYHOLDERS OF CLEARWIRE ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT, WHICH IS AVAILABLE NOW, AND THE PARTICIPANTS’ OTHER PROXY MATERIALS FILED WITH THE SEC WHEN THEY BECOME AVAILABLE, BECAUSE THEY CONTAIN IMPORTANT INFORMATION, INCLUDING ADDITIONAL INFORMATION RELATED TO THE PARTICIPANTS, CLEARWIRE AND THE PROPOSED SPRINT MERGER. The definitive proxy statement and all other proxy materials filed with the SEC are available at no charge on the SEC’s website at http://www.sec.gov. In addition, the definitive proxy statement is also available at no charge on the website of the Participants’ proxy solicitor at http://www.dfking.com/clwr.

Forward-looking Statements

Certain statements contained herein are forward-looking statements including, but not limited to, statements that are predications of or indicate future events, trends, plans or objectives. Undue reliance should not be placed on such statements because, by their nature, they are subject to known and unknown risks and uncertainties. Forward-looking statements are not guarantees of future activities and are subject to many risks and uncertainties. Due to such risks and uncertainties, actual events may differ materially from those reflected or contemplated in such forward-looking statements. Forward-looking statements can be identified by the use of the future tense or other forward-looking words such as “believe,” “expect,” “anticipate,” “intend,” “plan,” “should,” “may,” “will,” believes,” “continue,” “strategy,” “position” or the negative of those terms or other variations of them or by comparable terminology.

SOURCE: Crest Financial Limited